Intervertebral discs provide articulating means and mechanical stress absorption in the spine and further serve to permit controlled motion across vertebral segments. Vertebral discs degenerate progressively as a result of the natural aging process, and injury or disease, and with physical degeneration comes a loss in thickness or height of the disc, and a loss in their capacity to support a load and to absorb shock. Physically, disc degeneration can present in the form of the disc bulging material beyond its normal anatomical space or with collapse of the disc, both conditions being associated with spinal stenosis. Degenerative disc disease is variously associated with axial neck or back pain, a loss of normal spinal motion or increased abnormal motion, back pain, numbness, tingling, or weakness in one or more limbs.
In other instances a sudden physical stress on the spine can cause a defect to occur on the fibrous outer ring of the disc, the annulus fibrosis. In these cases the inner disc material, the nucleus pulposus, can rupture or protrude beyond the outer surface of the annulus, or shift outward a portion of the ring of the annulus fibrosis, resulting in an impingement on an adjacent neural structure. This is commonly referred to as a disc herniation, protrusion, or rupture, and typically causes symptoms similar to those of degenerative disc disease.
Nerve root impingements related to disc degeneration can occur throughout the spine but are most common in the lumbar and cervical regions. Most symptomatic disc degenerations occur posteriorly, and are thus particularly problematic as they are immediately adjacent to the spinal cord and nerve roots, and thereby prone to inducing neural impingement.
There are various treatment options for degenerative disc disease and disc herniations. Mild degenerative disc disease is often treated non-surgically, but more severe cases often require surgical treatment. These treatments may include the removal of the disc (discectomy), a reconditioning of the disc using a synthetic substance added to the nucleus (nucleoplasty), artificial total disc replacement (arthroplasty), or a spinal fusion procedure (arthrodesis). Recent trends in spine surgical development have focused on the replacement or repair of damaged discs with various biocompatible implants or repair devices. While a total disc arthroplasty in the cervical spine is presently done from an anterior surgical approach to the spine, a reconditioning of any disc may be achieved injecting an artificial nucleus pulposus material through a defect surgically created in the annulus fibrosis in the course of resecting compressing disc material.
Presently, current techniques for reconditioning the nucleus pulposus with a synthetic material or performing a total disc arthroplasty (disc replacement) require that a defect be made in the outer rim of the disc, the annulus fibrosis. The annulus defect may be several millimeters wide, as when injecting a nucleus reconditioning substance such as NuCore (Spine Wave, Inc., Shelton, Conn.), or it may be as large as several centimeters, as when doing a disc arthroplasty. Any defect in the annulus, however, can initiate a post-operative herniation or migration of the implanted reconditioning substance out of the normal interior space of the disc. This undesirable result can induce a compression of an adjacent neural structure and/or induce a collapse of the intervertebral disc.
Some improvements have been made in surgical approaches to disc damage or disease, as exemplified by U.S. Pat. App. No. 2006/0271198 of McAfee, U.S. Pat. App. No. 2005/0149046 of Friedman, and U.S. Pat. App. No. 2006/0074424 of Alleyne. There remains a need, however, specifically for approaches by which the inner portion, the nucleus pulposus, of the vertebral discs, particularly cervical discs, can be accessed and repaired, restored, or replaced without violating the annulus fibrosis of the disc.